1. Field of the Invention
The present invention relates to a piston-crank mechanism for use in automobile engines and so forth.
2. Description of the Related Art
Piston-crank mechanisms for converting reciprocating movement of a piston into rotational movement have been widely used in steam engines since the invention up to contemporary automobile engines. This piston-crank mechanism has sliding portions such as the sliding surface between the cylinder and the piston and bearing portions of crank pins, which produce frictional resistance forces, so that power loses due to severe variations in load, variations in frictional forces, and generation of heat are increased. These are known as causes of reduced transmission efficiencies and hastening of wear and tear in the piston, the cylinder, bearings, etc.
In order to improve the transmission efficiencies and prevent wear and tear in the piston, the cylinder, bearings, etc., various improvements in materials, structures, lubrication, cooling, and so forth have been conventionally made. A conventional piston-crank mechanism has been basically a structure shown in FIG. 7; however no innovative improvements on this mechanism have been made.
In a structure of a conventional piston-crank mechanism for one cylinder, as schematically shown in FIGS. 7a to 7d, a piston 101, a piston rod 106, and a crankshaft 103 are arranged on one straight line. At the top dead center of the piston 101 (FIG. 7a), a cylinder chamber 102 is just before the explosion process or the suction process while at the bottom dead center (FIG. 7c) is just before the exhaustion process or the compression process, and the piston 101 at both the positions is in an almost stationary state. In these positions, the crankshaft 103 is rotated in the "A" direction owing to the explosive force of another cylinder or inertial forces of the crankshaft 103 and a crank arm 104 integrated in the crankshaft 103; the bending moment is scarcely applied to the piston rod 106 and neither the side pressure nor the frictional force due to the side pressure are applied to the sliding surface "D" between the cylinder 102 and the piston 101 because connecting portions between the crank arm 104 and the connection rod 105 and between the connection rod 105 and the piston rod 106 are pivoted with a crank pin 107 and a piston pin 108, respectively.
On the other hand, in an intermediate position from the top to the bottom of the piston stroke (FIG. 7b), the rotation "A" of the crankshaft 103 mainly depends on the downward thrust of the piston 101 shown in the drawing, i.e., explosive forces in the cylinder 102, in the explosion process. At this time, the rotational force is applied to the crank arm 104 via the connection rod 105 which is much inclined ".theta." toward the piston rod 106. Since the piston rod 106 is fixed to the piston 101 in unison, the reaction force of the rotational driving force strongly pushing the crank arm 104 with the connection rod 105 is applied to the piston pin 108 to apply the bending moment to the piston rod 106. Thereby, the high side pressure and the frictional force accompanied thereby are applied to the sliding surface
As shown in "P01" of FIG. 8 illustrating variations in the side pressure and the frictional force due to the side pressure in the crank pin 107, pressures are low in the top and bottom dead centers (FIGS. 7a and 7c) while is high in the intermediate position (FIG. 7b) of the explosion process.
In the suction process of the piston-cylinder, the driving direction is switched so that the crank arm 104 drives the connection rod 105 which in turn pushes up the piston rod 106 in the axial direction thereof. At this time, the side pressure and the frictional force accompanied thereby are applied to the sliding surface "D" by the inclination ".theta." of the connection rod 105 to the piston rod 106. Since the resistance force against the suction is smaller than the driving force from the crank arm 104, the pressure is rather lower as shown in "P02" of FIG. 8; however just like "P01", the maximum pressure is shown in the intermediate position of the stroke of the piston 101.
In FIG. 7d that is the exhaustion process or the compression process of the piston 101, the crank arm 104 is rotated in the "A" direction of the crankshaft 103 owing to the explosive force of another cylinder or inertial forces of the crankshaft 103 or a crank arm 104 so as to push the sliding portion of the crank pin 107 which is the connecting portion to the connecting rod 105. Since this pushing force is used only for the exhaustion or the compression by pushing up the connecting rod 105, the piston rod 106, and the piston 101, it is not so large as that in the explosion process, resulting in the same line "P02" as that of the suction process.
Among respective processes of suction, compression, explosion, and exhaustion, in the intermediate positions (FIGS. 7b and 7d) in which the speed of the piston 101 is the highest, the side pressure/the frictional force in the sliding surface "D" between the piston 101 and the cylinder 102 is the maximum as shown in FIG. 8.
The above-mentioned problem of the side pressure/the frictional force in the sliding surface "D" between the piston 101 and the cylinder 102 also arises almost similarly in a piston-crank mechanism for use in fuel-injection-type engines in which suction and compression of fuel are not performed.
As described above, in the conventional piston-crank mechanism, since in the intermediate positions in which the speed of the piston 101 is the highest, the side pressure/the frictional force in the sliding surface "D" between the piston 101 and the cylinder 102 is the maximum, the cylinder 102 and the piston 101 sliding within the cylinder 102 have to tolerate the extremely severe state. In particular, in the intermediate portion of the cylinder 102, the speed and the side pressure/the frictional force of the piston 101 are the maximums, so that the state thereof is most severe.
When a piston-cylinder after long term use or having scoring is disassembled, the intermediate portion "C" of the cylinder 102 and the sliding surface "D" of the piston 101 are severely damaged as shown in FIG. 9a, so that the severe state in which the speed and the side pressure/the frictional force of the piston 101 are the maximums can be supposed. The speed and the side pressure/the frictional force of the piston 101 not only reduce an operating life of the piston 101-cylinder 102 but also deteriorate the transmission efficiency of the piston-cylinder mechanism and engine efficiencies because some engine power is consumed by the useless side pressure/the frictional force.
On the other hand, when the piston 101 approaches the top and bottom dead centers of the reciprocating stroke thereof, the frictional force in the sliding surface "D" between the piston 101 and the cylinder 102 is small so as to bring about such a state that brakes are not applied to overrunning of the piston 101. Therefore, the crank arm 104 is meaninglessly pushed and pulled in the top and bottom dead centers, so that bearings of the crankshaft 103, the crank pin 107, and the piston pin 108 are laterally pressed on impact to be hastened to damages of these parts in vain.
When a crank pin after long term use or having scoring is disassembled, the damaged surfaces "E" of the crank pin 107 are concentrated in an angular position in which the above-mentioned impact is produced, as shown in FIG. 9b, thereby, the above-mentioned situation can be confirmed. This impactive force also reduces the transmission efficiency of the piston-cylinder mechanism and engine efficiencies by consuming some engine power.
The above-mentioned arrangement of the piston 101, the piston rod 106, and the crankshaft 103 on one straight line has been also a restriction on engine design.
In order to solve the above-mentioned problems, the inventor of the present invention invented a novel piston-crank mechanism earlier, so that Japanese Patent No. 2958310 was granted, which was issued Oct. 6, 1999. In the piston-crank mechanism according to Japanese Patent No. 2958310, a guide link swingably pivoted on a fixed point and a piston rod are connected with a free link while a connecting rod is pivoted on the guide link, wherein respective links are arranged and connected so that in an intermediate position of the stroke of a piston, the pivoting point between the free link and the guide link agrees with or approaches an axial line of the piston.